Technical Field
The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to a system and method for detecting a fault in a capacitive return electrode for use in electrosurgery.
Description of Related Art
Electrosurgery is the application of electricity and/or electromagnetic energy to cut or modify biological tissue during a surgical procedure. Generally, electrosurgery utilizes an electrosurgical generator, an active electrode, and a return electrode. The electrosurgical generator generates an electromagnetic wave (referred to herein as “electrosurgical energy”), typically above 100 kilohertz, between the active and return electrodes when applied to tissue. The electromagnetic wave created therebetween dissipates energy as heat as it travels between the electrodes. The electrosurgical energy usually has a frequency above 100 kilohertz to avoid muscle and/or nerve stimulation.
During electrosurgery, current generated by the electrosurgical generator is conducted through the patient's tissue disposed between the two electrodes. The current causes the tissue to heat up as the electromagnetic wave overcomes the tissue's impedance. Although many other variables affect the total heating of the tissue, usually more current density directly correlates to increased heating. The electrosurgical energy is typically used for cutting, dissecting, ablating, coagulating, and/or sealing tissue.
The two basic types of electrosurgery employed are monopolar and bipolar electrosurgery; however, both types use an “active” and a “return” electrode. In bipolar electrosurgery, the surgical instrument includes an active electrode and a return electrode on the same instrument or in very close proximity, usually causing current to flow through a smaller amount of tissue. In monopolar electrosurgery, the return electrode is located elsewhere on the patient's body and is usually not part of the electrosurgical instrument itself. In monopolar electrosurgery, the return electrode is part of a device usually referred to as a return pad.
The return pad may have one or more return electrodes. The return electrodes are typically in the form of pads adhesively adhered to the patient and are placed remotely from the active electrode to carry the current back to the generator. The return electrodes usually have a large patient contact surface area to minimize heating at that site since the smaller the surface area, the greater the current density and the greater the intensity of the heat. That is, the area of the return electrode that is adhered to the patient is important because it is the current density of the electrical signal that heats the tissue. A larger surface contact area is desirable to reduce localized heat intensity. Return electrodes are typically sized based on assumptions of the maximum current utilized during a particular surgical procedure and the duty cycle (i.e., the percentage of time the generator is on). The first types of return electrodes were in the form of large metal plates covered with conductive jelly. Later, adhesive electrodes were developed with a single or dual-split metal foil covered with conductive jelly or conductive adhesive.
Another type of return pad is the capacitive return pad. A capacitive return pad has one or more capacitive return electrodes. A capacitive return electrode usually includes two layers of metal foil as mentioned above with the addition of a dielectric material disposed in between the metal foils. The dielectric material is designed to be positioned between the top and bottom metal foils. The capacitive return electrode allows electrosurgical energy of sufficient frequency to pass through the capacitance of the pad and the patient but prevents DC or very low frequencies from passing through the return pad. The addition of the dielectric material generally causes the heat to be more evenly distributed throughout the capacitive return pad.
The effects of the electrosurgical energy is also affected by other factors, including the patient's age, weight, the type of tissue being modified, and the desired tissue effect. Different tissue effects occur by varying the voltages, currents, duty cycle, and frequencies used.